Phase shift mask blank, manufacturing method thereof, and phase shift mask

ABSTRACT

Provided is a phase shift mask blank including a substrate, and a phase shift film thereon, the phase shift film composed of a material containing silicon and nitrogen and free of a transition metal, exposure light being KrF excimer laser, the phase shift film consisting of a single layer or a plurality of layers, the single layer or each of the plurality of layers having a refractive index n of at least 2.5 and an extinction coefficient k of 0.4 to 1, with respect to the exposure light, and the phase shift film having a phase shift of 170 to 190° and a transmittance of 4 to 8%, with respect to the exposure light, and a thickness of up to 85 nm.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application Nos. 2019-067113 and 2019-111054 filed inJapan on Mar. 29, 2019 and Jun. 14, 2019, respectively, the entirecontents of which are hereby incorporated by reference.

TECHNICAL FIELD

The invention relates to a phase shift mask blank and a phase shiftmask, typically used for manufacturing a semiconductor integratedcircuit, and a manufacturing method of a phase shift mask blank.

BACKGROUND ART

In a photolithography technique used in a semiconductor technology, aphase shift method is used as one of a resolution enhancementtechnology. The phase shift method is, for example, a method using aphotomask in which a phase shift film is formed on a substrate, and is acontrast enhancing method by forming a phase shift film pattern disposedon a transparent substrate being a photomask substrate which istransparent to exposure light, and utilizing interference of lights. Thephase shift film pattern has a phase shift of approximately 180° that isa difference between a phase through the phase shift film and a phasethrough a portion that is not formed the phase shift film, in otherword, a phase through air having a length same as the thickness of thephase shift film. A halftone phase shift mask is one of the photomasksemploying such method. The halftone phase shift mask includes atransparent substrate made of quartz or the like which is transparent toexposure light, and a mask pattern of a halftone phase shift film whichis formed on the transparent substrate and has a phase shift ofapproximately 180° to a phase through a portion not formed the phaseshift film, and a transmittance substantively insufficient to contributeto exposure. Until now, as a phase shift film for a phase shift mask, afilm containing molybdenum and silicon is mostly used (JP-A H07-140635(Patent Document 1)).

CITATION LIST

Patent Document 1: JP-A H07-140635

Patent Document 2: JP-A 2007-33469

Patent Document 3: JP-A 2007-233179

Patent Document 4: JP-A-2007-241065

DISCLOSURE OF INVENTION

In case that exposure light is KrF excimer laser (wavelength of 248 nm),a phase shift film having a transmittance of 6%, a phase shift ofapprox. 180° and a thickness of approx. 100 nm is generally used in aphase shift mask employed a film containing molybdenum and silicon.Recently, for a phase shift film used with ArF excimer laser (wavelengthof 193 nm) as exposure light, a phase shift film of silicon nitride hasbeen used for the purposes of minimizing film thickness and enhancingwashing resistance and light resistance. Although not much as exposurelight of ArF excimer laser, also when KrF excimer laser is used as theexposure light, the phase shift film having high washing resistance andhigh light resistance and being hard to generate haze is needed.

When KrF excimer laser is used as exposure light with silicon nitride,it is necessary to adjust the content ratio of nitrogen and silicon inaccordance with its wavelength for forming a film satisfying apredetermined phase shift and a predetermined transmittance with KrFexcimer laser. Further, in consideration of inclination of the patternduring processing into the phase shift mask, and a cross-sectional shapeof the pattern, a thinner film having a uniform composition is desired.When exposure light is ArF excimer laser, silicon nitride containingmore nitrogen has a higher refractive index n and a smaller extinctioncoefficient k. Thus, a phase shift film having a nitrogen content ashigh as possible has been proposed.

The present invention has been made to solve the above problems, and anobject of the present invention is to provide a phase shift mask blankand a phase shift mask, including a thin phase shift film, andsatisfying a requirement for pattern miniaturization, which isadvantageous in terms of patterning and reduction of three-dimensionaleffect, and with satisfying necessary phase shift and transmittance forthe phase shift film even when exposure light is KrF excimer laserhaving a wavelength of 246 nm. Further, another object of the presentinvention is to provide a manufacturing method of the phase shift maskblank.

The inventor has found that: when the exposure light is KrF excimerlaser, unlike the ArF excimer laser, silicon nitride has a highestrefractive index n at a content (at %) ratio Si/N of about 53/47; and athin film cannot be achieved by simply increasing of nitrogen content.Further, the inventor has found that regarding silicon nitride forexposure light of KrF excimer laser, in a phase shift mask blank forexposure with KrF excimer laser having a wavelength of 248 nm, a phaseshift film having a composition containing silicon and nitrogen and freeof a transition metal, and satisfying a predetermined refractive index nand a predetermined extinction coefficient k or having a nitrogen ratioin a predetermined range can provide a phase shift amount (phase shift)of 170 to 190°, and particularly, a transmittance of 4 to 8%, withrespect to the exposure light, with a thickness of up to 85 nm, therebya phase shift mask blank and a phase shift mask including a thinnerphase shift film are obtained.

In one aspect, the invention provides a phase shift mask blank includinga substrate, and a phase shift film thereon, the phase shift filmcomposed of a material containing silicon and nitrogen and free of atransition metal, wherein

exposure light is KrF excimer laser,

the phase shift film consists of a single layer or a plurality oflayers, the single layer or each of the plurality of layers has arefractive index n of at least 2.5 and an extinction coefficient k of0.4 to 1, with respect to the exposure light, and

the phase shift film has a phase shift of 170 to 190° and atransmittance of 4 to 8%, with respect to the exposure light, and athickness of up to 85 nm.

Preferably, the single layer or each of the plurality of layers has acontent ratio N/(Si+N) within a range of 0.43 to 0.53, the ratioN/(Si+N) representing nitrogen content (at %) to the sum of silicon andnitrogen contents (at %).

In other aspect, the invention provides a phase shift mask blankincluding a substrate, and a phase shift film thereon, the phase shiftfilm composed of a material containing silicon and nitrogen and free ofa transition metal, wherein

exposure light is KrF excimer laser,

the phase shift film consists of a single layer or a plurality oflayers, at least part of the single layer or at least part of theplurality of layers has a content ratio N/(Si+N) within a range of 0.43to 0.53, the ratio N/(Si+N) representing nitrogen content (at %) to thesum of silicon and nitrogen contents (at %), and

the phase shift film has a phase shift of 170 to 190° with respect tothe exposure light.

In other aspect, the invention provides a method of manufacturing thephase shift mask blank of any one of claims 1 to 3, including the stepof:

forming the phase shift film by reactive sputtering using asilicon-containing target and nitrogen gas, wherein

in the forming step, a flow rate of the nitrogen gas is set to a valueof −20% to +20% of the flow rate imparting the highest refractive indexn, with respect to the exposure light, of the phase shift film, andmaintained constant or varied continuously or stepwise, the flow rateimparting the highest refractive index n being obtained from varying theflow rate from low rate to high rate.

Preferably, in the forming step, the flow rate of the nitrogen gas isset to the flow rate imparting the highest refractive index n, withrespect to the exposure light, of the phase shift film, and maintainedconstant.

Preferably, the sputtering is a magnetron sputtering, and thesilicon-containing target is silicon target.

In other aspect, the invention provides a phase shift mask manufacturedby using the phase shift mask blank.

ADVANTAGEOUS EFFECTS OF THE INVENTION

According to the invention, there is provided a phase mask blank and aphase shift mask having a thinner phase shift film which is advantageousin terms of patterning and exposure, with satisfying necessary phaseshift and transmittance for the phase shift film used in exposure lightof KrF excimer laser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-sectional views illustrating an exemplaryphase shift mask blank and a phase shift mask of the invention.

FIGS. 2A to 2C are cross-section views illustrating other examples of aphase shift mask blank of the invention.

FIG. 3 is a graph plotting refractive indexes n with respect to flowrates of nitrogen gas in Example 1.

FIG. 4 is a graph plotting extinction coefficients k with respect toflow rates of nitrogen gas in Example 1.

FIG. 5 is a graph plotting refractive indexes n with respect to contentratios N/(Si+N) in Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The phase shift mask blank of the invention includes a transparentsubstrate such as a quartz substrate, and a phase shift film that isprovided on the transparent substrate. The phase shift mask of theinvention includes a transparent substrate such as a quartz substrate,and a mask pattern (photomask pattern) of a phase shift film which isprovided on the transparent substrate.

The transparent substrate in the invention is preferably, for example, a6 inch square, 0.25 inch thick transparent substrate, called 6025substrate specified by the SEMI standard, which is often denoted by a152 mm square, 6.35 mm thick transparent substrate, according to the SIunit system.

FIG. 1A is a cross-sectional view illustrating an exemplary phase shiftmask blank of the invention. In this embodiment, a phase shift maskblank 100 includes a transparent substrate 10, and a phase shift film 1formed on the transparent substrate 10. FIG. 1B is a cross-sectionalview illustrating an exemplary phase shift mask of the invention. Inthis embodiment, the phase shift mask 101 includes the transparentsubstrate 10, and a phase shift film pattern 11 formed on thetransparent substrate 10. A phase shift mask can be obtained by using aphase shift mask blank and forming a pattern of its phase shift film.

The phase shift film in the invention, with a prescribed thickness, hasa predetermined phase shift amount (phase shift) and a predeterminedtransmittance, with respect to exposure light of KrF excimer laser(wavelength: 248 nm). The phase shift film of the invention is composedof a material containing silicon and nitrogen and free of a transitionmetal. To improve washing resistance of the film, it is effective to addoxygen to the phase shift film. Thus, the material containing siliconand nitrogen and free of a transition metal may contain oxygen inaddition to silicon and nitrogen. However, the refractive index n of thefilm is reduced when oxygen is added, so, the film thickness tends to beincreased. Therefore, as the material containing silicon and nitrogenand free of a transition metal, a material consisting essentially ofsilicon and nitrogen (a material consisting of two of the elements andinevitable impurities) is preferable.

The phase shift film may consist of a single layer or a plurality oflayers which is designed so as to satisfy necessary phase shift andtransmittance for the phase shift film. In each case of the single layerand the plurality of layers, the single layer or each of the pluralityof layers may be a single composition layer in which the compositiondoes not vary in a thickness direction, or a compositionally gradedlayer in which the composition varies in a thickness direction.

In the single layer or each of the plurality of layers of the inventivephase shift film, a refractive index n is preferably at least 2.5, morepreferably at least 2.55. The upper limit of the refractive index n isnormally up to 2.7. In the single layer or each of the plurality oflayers of the inventive phase shift film, a extinction coefficient k ispreferably at least 0.4, more preferably at least 0.5, and preferably upto 1, more preferably up to 0.8.

In the phase shift film of the invention, a content ratio N/(Si+N) ispreferably at least 0.43, more preferably 0.45, and preferably up to0.53, more preferably up to 0.5 in at least part of the single layer,particularly in the whole of the single layer when the phase shift filmis constructed by a single layer, or in at least part of the pluralityof layers, particularly in each of the plurality of layers (in alllayers) when the phase shift film is constructed by a plurality oflayers. The ratio N/(Si+N) represents nitrogen content (at %) to the sumof silicon and nitrogen contents (at %). Notably, the compositionallygraded layer is employed, it is preferable that graded range of thecomposition is within the above content ratio range. In case that thesingle layer or each of the plurality of layers contains oxygen, anoxygen content is preferably up to 30 at %, more preferably up to 10 at%, most preferably up to 5 at %.

The phase shift of the exposure light which passes through the phaseshift film in the invention may be enough to be able to increasecontrast at the boundary between an area having the phase shift film(phase shift area) and an area without the phase shift film, as a resultof phase shift due to interference of exposure lights passing throughthe respective areas. The phase shift may be at least 170° and up to190°. Meanwhile, a transmittance of the phase shift film in theinvention may be at least 4% and up to 8% with respect to exposurelight. The phase shift film in the invention may have the phase shiftand the transmittance with respect to KrF excimer laser (wavelength: 248nm), controlled within the aforementioned range.

When a whole thickness of the phase shift film is thin, fine patternscan be readily formed. Thus, the whole thickness of the phase shift filmin the invention may be up to 85 nm, preferably up to 80 nm. Meanwhile,the lower limit of the thickness of the phase shift film may be set solong as the desired optical characteristics may be obtained withexposure light, and is typically at least 50 nm, however not limitedthereto.

The phase shift film in the invention may be formed by known methods forforming film. The phase shift film is preferably formed by sputtering bywhich highly homogenous film is easily obtainable, and the sputteringmay be either DC sputtering or RF sputtering, and preferably magnetronsputtering. Target and sputtering gas are properly selected depending onkind and composition of the layer to be formed. Examples of the targetinclude a silicon-containing target such as silicon target, siliconnitride target, and a target containing both of silicon and siliconnitride. The nitrogen content may be controlled by reactive sputteringusing nitrogen gas for a reactive gas as a sputtering gas under properlycontrolling an amount of feeding. Rare gases such as helium gas, neongas and argon gas are also employable as the sputtering gas.

When the phase shift film of the invention is formed by reactivesputtering using a silicon-containing target and nitrogen gas, the phaseshift film is formed preferably at a flow rate of the nitrogen gas thatis set to a value of −20% to +20% of the flow rate imparting the highestrefractive index n, with respect to the exposure light, particularly ata flow rate of the nitrogen gas that is set to a value of the flow rateimparting the highest refractive index n, with respect to the exposurelight. A phase shift film having a phase shift of 170 to 190 ° and atransmittance of 4 to 8% can be formed thinner by this way. The flowrate imparting the highest refractive index n may be determinedbeforehand by confirming a variation of refractive index n of siliconnitride while the flow rate is varied from low rate to high rate. Atthis time, sputtering conditions (power applied to the target, flow rateof other sputter gase, sputter pressure, etc.) other than the flow rateof the nitrogen gas are fixed (constant). Notably, when the film isactually formed, the flow rate may be maintained constant or variedcontinuously or stepwise.

The phase shift film consisting multiple layers may include an oxidizedsurface layer formed as the outermost layer on the top face (on the sideremote from the transparent substrate), for the purpose of suppressingchange of properties of the phase shift film. The oxidized surface layermay have an oxygen content of at least 20 at %, preferably at least 50at %. Examples of methods for forming the oxidized surface layerspecifically include atmospheric oxidation (natural oxidation); andforced oxidation treatment such as treatment of a sputtered film withozone gas or ozonated water, or heating at least 300° C. in anoxygen-containing atmosphere such as oxygen gas atmosphere, by heatingin oven, lamp annealing or laser heating. The oxidized surface layerpreferably has a thickness of up to 10 nm, more preferably up to 5 nm,most preferably up to 3 nm. An effect of the oxidized surface layer isobtainable typically with a thickness of at least 1 nm. While theoxidized surface layer may be formed by sputtering under an increasedoxygen amount, the oxidized surface layer is more preferably formed bythe aforementioned atmospheric oxidation or oxidation treatment in termsof obtaining the layer with fewer defects.

The phase shift mask blank of the invention may include a second layerconsisting of a single layer or multiple layers, and is formed over thephase shift film. The second layer is usually provided adjacent to thephase shift film. The second layer is specifically exemplified by alight shielding film, a combination of a light shielding film and anantireflection film, and a process-aid film that functions as a hardmask in the process of patterning the phase shift film. In case where athird layer is employed as described below, the second layer may be usedas a process-aid film that functions as an etching stopper (etchingstopper film) in the process of patterning the third layer. Material ofthe second layer is preferably a chromium-containing material.

This embodiment is specifically exemplified by a phase shift mask blankillustrated in FIG. 2A. FIG. 2A is a cross-sectional view illustratingan exemplary phase shift mask blank of the invention. In thisembodiment, a phase shift mask blank 100 includes a transparentsubstrate 10, a phase shift film 1 formed on the transparent substrate10, and a second layer 2 formed on the phase shift film 1.

The phase shift mask blank of the invention may include a lightshielding film or an etching mask film which functions as a hard maskwhen a pattern is formed to a phase shift film, as the second layer,provided over the phase shift film. Alternatively, a light shieldingfilm and an antireflection film may be combined to form the secondlayer. The second layer including a light shielding film can provide anarea that is fully block the exposure light in a phase shift mask. Thelight shielding film and the antireflection film may also be used as aprocess-aid film in the etching. There are many reports regarding filmstructure and materials for the light shielding film and antireflectionfilm (JP-A 2007-33469 (Patent Document 2), JP-A 2007-233179 (PatentDocument 3), for example). Preferred film structure having the lightshielding film and the antireflection film combined therein isexemplified by a structure in which a light shielding film composed of achromium-containing material is provided, and an antireflection filmcomposed of a chromium-containing material for reducing reflection fromthe light shielding film is further provided. The light shielding filmand the antireflection film may consist of a single layer or multiplelayers. Examples of the chromium-containing material of the lightshielding film and the antireflection film include chromium (simplesubstance), and a chromium compound such as chromium oxide (CrO),chromium nitride (CrN), chromium carbide (CrC), chromium oxynitride(CrON), chromium oxycarbide (CrOC), chromium nitride carbide (CrNC) andchromium oxynitride carbide (CrONC). Notebly, the chemical formulae thatrepresent the chromium-containing materials merely denote constituentelements, rather than compositional ratios of the constituent elements(the same shall apply to the chromium-containing materials hereinafter).

For the second layer as the light shielding film, or the combination ofa light shielding film and an antireflection film, the chromium compoundin the light shielding film has a chromium content of preferably atleast 40 at %, more preferably at least 60 at %, and preferably lessthan 100 at %, more preferably up to 99 at %, most preferably up to 90at %. The oxygen content is preferably up to 60 at %, more preferably upto 40 at %, and preferably at least 1 at %. The nitrogen content ispreferably up to 50 at %, more preferably up to 40 at %, and preferablyat least 1 at %. The carbon content is preferably up to 20 at %, morepreferably up to 10 at %, and if the etching rate is necessarilyadjusted, preferably at least 1 at %. In this case, a total content ofchromium, oxygen, nitrogen and carbon is preferably at least 95 at %,more preferably at least 99 at %, and most preferably 100 at %.

For the second layer as the combination of a light shielding film and anantireflection film, the antireflection film is preferably composed of achromium compound, and the chromium compound has a chromium content ofpreferably at least 30 at %, more preferably at least 35 at %, and up to70 at %, more preferably up to 50 at %. The oxygen content is preferablyup to 60 at %, and preferably at least 1 at %, more preferably at least20 at %. The nitrogen content is preferably up to 50 at %, morepreferably up to 30 at %, and preferably at least 1 at %, morepreferably at least 3 at %. The carbon content is preferably up to 20 at%, more preferably up to 5 at %, and if the etching rate is necessarilyadjusted, preferably at least 1 at %. In this case, a total content ofchromium, oxygen, nitrogen and carbon is preferably at least 95 at %,more preferably at least 99 at %, most preferably 100 at %.

For the second layer as the light shielding film, or the combination ofa light shielding film and an antireflection film, the second layer hasa thickness of usually 20 to 100 nm, and preferably 40 to 70 nm. A totaloptical density of the phase shift film and the second layer arepreferably at least 2.0, more preferably at least 2.5, most preferablyat least 3.0, with respect to exposure light.

Over the second layer of the phase shift mask blank of the invention, athird layer consisting of a single layer or multiple layers may beprovided. The third layer is usually provided adjacent to the secondlayer. The third layer is specifically exemplified by a process-aid filmthat functions as a hard mask in the process of patterning the secondlayer, a light shielding film, and a combination of a light shieldingfilm and an antireflection film. A material composing the third layer ispreferably a silicon-containing material, particularly asilicon-containing material free of chromium.

This embodiment is specifically exemplified by a phase shift mask blankillustrated in FIG. 2B. FIG. 2B is a cross-sectional view illustratingan exemplary phase shift mask blank of the invention. In thisembodiment, the phase shift mask blank 100 includes a transparentsubstrate 10, a phase shift film 1 formed on the transparent substrate10, a second layer 2 formed on the phase shift film 1, and a third layer3 formed on the second layer 2.

For the second layer as the light shielding film, or the combination ofa light shielding film and an antireflection film, a process-aid film(etching mask film) which functions as a hard mask in the process ofpatterning the second layer may be provided as the third layer. In casewhere a fourth layer is employed as described below, the third layer maybe used as a process-aid film that functions as an etching stopper(etching stopper film) in the process of patterning the fourth layer.The process-aid film is preferably composed of a material that differsin etching characteristics from the second layer, such as a materialresistant to chlorine-based dry etching for a chromium-containingmaterial, in particular, a silicon-containing material which can beetched by fluorine-containing gases such as SF₆ and CF₄. Examples of thesilicon-containing material include silicon (simple substance), and asilicon compound such as a material containing silicon, and either orboth of nitrogen and oxygen, a material containing silicon and atransition metal, and a material containing silicon, and either or bothof nitrogen and oxygen with a transition metal. Examples of thetransition metal include molybdenum, tantalum and zirconium.

For the third layer as the process-aid film, the process-aid film ispreferably composed of a silicon compound. The silicon compound has asilicon content of preferably at least 20 at %, more preferably at least33 at %, and preferably up to 95 at %, and more preferably up to 80 at%. The nitrogen content is preferably up to 50 at %, more preferably upto 30 at %, and preferably at least 1 at %. The oxygen content ispreferably up to 70 at %, more preferably up to 66 at %, and if theetching rate is necessarily adjusted, preferably at least 1 at %, morepreferably at least 20 at %. A transition metal may be contained or notin the third layer. When the transition metal is contained thetransition metal content is preferably up to 35 at %, more preferably upto 20 at %. In this case, a total content of silicon, oxygen, nitrogenand transition metal is preferably at least 95 at %, more preferably atleast 99 at %, most preferably 100 at %.

For the second layer as the light shielding film, or the combination ofa light shielding film and an antireflection film, and for the thirdlayer as the process-aid film, the second layer has a thickness ofusually 20 to 100 nm, and preferably 40 to 70 nm, and the third layertypically has a thickness of usually 1 to 30 nm, and preferably 2 to 15nm. A total optical density of the phase shift film and the second layerare preferably at least 2.0, more preferably at least 2.5, mostpreferably at least 3.0, with respect to exposure light.

For the second layer as the process-aid film, a light shielding film maybe provided as the third layer. The light shielding film in combinationwith the antireflection film may be provided as the third layer. In thiscase, the second layer may be used as a process-aid film (etching maskfilm) that functions as a hard mask in the process of patterning thephase shift film, and as a process-aid film (etching stopper film) inthe process of patterning the third layer. The process-aid film isexemplified by a film composed of a chromium-containing material, suchas disclosed in JP-A 2007-241065 (Patent Document 4). The process-aidfilm may consist of a single layer or multiple layers. Examples of thechromium-containing material of the process-aid film include chromium(simple substance), and a chromium compound such as chromium oxide(Cr0), chromium nitride (CrN), chromium carbide (CrC), chromiumoxynitride (CrON), chromium oxycarbide (CrOC), chromium nitride carbide(CrNC) and chromium oxynitride carbide (CrONC).

For the second layer as the process-aid film, the chromium compound inthe second layer has a chromium content of preferably at least 40 at %,more preferably at least 50 at %, and preferably up to 100 at %, morepreferably up to 99 at %, most preferably up to 90 at %. The oxygencontent is preferably up to 60 at %, more preferably up to 55 at %, andif the etching rate is necessarily adjusted, preferably at least 1 at %.The nitrogen content is preferably up to 50 at %, more preferably up to40 at %, and preferably at least 1 at %. The carbon content ispreferably up to 20 at %, more preferably up to 10 at %, and if theetching rate is necessarily adjusted, preferably at least 1 at %. Inthis case, a total content of chromium, oxygen, nitrogen and carbon ispreferably at least 95 at %, particularly at least 99 at %, mostpreferably 100 at %.

The light shielding film and the antireflection film as the third layerare preferably composed of a material that differs in etchingcharacteristics from the second layer, such as a material resistant tochlorine-based dry etching for a chromium-containing material, inparticular, a silicon-containing material which can be etched byfluorine-containing gases such as SF₆ and CF₄. Examples of thesilicon-containing material include silicon (simple substance), and asilicon compound such as a material containing silicon, and either orboth of nitrogen and oxygen, a material containing silicon and atransition metal, and a material containing silicon, and either or bothof nitrogen and oxygen with a transition metal. Examples of thetransition metal include molybdenum, tantalum and zirconium.

For the third layer as the light shielding film, or the combination of alight shielding film and an antireflection film, the light shieldingfilm and the antireflection film are preferably composed of a siliconcompound. The silicon compound has a silicon content of preferably atleast 10 at %, more preferably at least 30 at %, and preferably lessthan 100 at %, more preferably up to 95 at %. The nitrogen content ispreferably up to 50 at %, preferably up to 40 at %, and most preferablyup to 20 at %, and if the etching rate is necessarily adjusted,preferably at least 1 at %. The oxygen content is preferably up to 60 at%, more preferably up to 30 at %, and if the etching rate is necessarilyadjusted, preferably at least 1 at %. The transition metal content ispreferably up to 35 at %, preferably up to 20 at %, and preferably atleast 1 at %. In this case, a total content of silicon, oxygen, nitrogenand transition metal is preferably at least 95 at %, more preferably atleast 99 at %, most preferably 100 at %.

For the second layer as the process-aid film, and for the third layer asthe light shielding film, or the combination of a light shielding filmand an antireflection film, the second layer has a thickness of usually1 to 20 nm, and preferably 2 to 10 nm, and the third layer has athickness of usually 20 to 100 nm, and preferably 30 to 70 nm. A totaloptical density of the phase shift film, the second layer and the thirdlayer are preferably at least 2.0, more preferably at least 2.5, mostpreferably at least 3.0, with respect to exposure light.

Over the third layer of the phase shift mask blank of the invention, afourth layer consisting of a single layer or multiple layers may beprovided. The fourth layer is usually provided adjacent to the thirdlayer. The fourth layer is specifically exemplified by a process-aidfilm that functions as a hard mask in the process of patterning thethird layer. A material of the fourth layer is preferably achromium-containing material.

This embodiment is specifically exemplified by a phase shift mask blankillustrated in FIG. 2C. FIG. 2C is a cross-sectional view illustratingan exemplary phase shift mask blank of the invention. In thisembodiment, the phase shift mask blank 100 includes a transparentsubstrate 10, a phase shift film 1 formed on the transparent substrate10, a second layer 2 formed on the phase shift film 1, a third layer 3formed on the second layer 2, and a fourth layer 4 formed on the thirdlayer 3.

For the third layer as the light shielding film, or the combination of alight shielding film and an antireflection film, a process-aid film(etching mask film) which functions as a hard mask in the process ofpatterning the third layer may be provided as the fourth layer. Theprocess-aid film is preferably composed of a material that differs inetching characteristics from the third layer, such as a materialresistant to fluorine-based dry etching for a silicon-containingmaterial, in particular, a chromium-containing material which can beetched by chlorine-based gases containing oxygen. Thechromium-containing material is exemplified by chromium (simplesubstance), and a chromium compound such as chromium oxide (CrO),chromium nitride (CrN), chromium carbide (CrC), chromium oxynitride(CrON), chromium oxycarbide (CrOC), chromium nitride carbide (CrNC) andchromium oxynitride carbide (CrONC).

For the fourth layer as the process-aid film, the fourth layer has achromium content of preferably at least 40 at %, more preferably atleast 50 at %, and preferably up to 100 at %, more preferably up to 99at %, most preferably up to 90 at %. The oxygen content is preferably upto 60 at %, more preferably up to 40 at %, and if the etching rate isnecessarily adjusted, preferably at least 1 at %. The nitrogen contentis preferably up to 50 at %, more preferably up to 40 at %, and if theetching rate is necessarily adjusted, preferably at least 1 at %. Thecarbon content is preferably up to 20 at %, more preferably up to 10 at%, and if the etching rate is necessarily adjusted, preferably at least1 at %. In this case, a total content of chromium, oxygen, nitrogen andcarbon is preferably at least 95 at %, more preferably at least 99 at %,most preferably 100 at %.

For the second layer as the process-aid film, for the third layer as thelight shielding film, or the combination of a light shielding film andan antireflection film, and for the fourth layer as the process-aidfilm, the second layer has a thickness of usually 1 to 20 nm, andpreferably 2 to 10 nm, the third layer has a thickness of usually 20 to100 nm, and preferably 30 to 70 nm, and the fourth layer has a thicknessof usually 1 to 30 nm, and preferably 2 to 20 nm. A total opticaldensity of the phase shift film, the second layer and the third layerare preferably at least 2.0, more preferably at least 2.5, mostpreferably at least 3.0, with respect to exposure light.

The film composed of the chromium-containing material for the secondlayer and the fourth layer may be formed by reactive sputtering using atarget such as chromium target, or a target containing chromium that isadded one or more elements selected from the group consisting of oxygen,nitrogen and carbon, and using a sputtering gas containing a rare gassuch as Ar, He and Ne that is properly added with a reactive gasselected from the group consisting of an oxygen-containing gas, anitrogen-containing gas and a carbon-containing gas, according to acomposition of the film to be formed.

Meanwhile, the film composed of the silicon-containing material for thethird layer may be formed by reactive sputtering using a target such asa silicon target, a silicon nitride target, a target containing both ofsilicon and silicon nitride, a transition metal target, and a compositetarget of silicon and transition metal, and using a sputtering gascontaining a rare gas such as Ar, He and Ne that is properly added witha reactive gas selected from the group consisting of anoxygen-containing gas, a nitrogen-containing gas and a carbon-containinggas, according to a composition of the film to be formed.

The phase shift mask of the invention may be manufactured by any ofusual methods from the phase shift mask blank. From an exemplary phaseshift mask blank including a film composed of a chromium-containingmaterial formed as a second layer on a phase shift film, the phase shiftmask may be manufactured typically by the following processes.

First, an electron beam resist film is formed on the second layer of thephase shift mask blank, a pattern is drawn by electron beam, followed bya predetermined operation of development, to obtain a resist pattern.Next, the obtained resist pattern is used as an etching mask, and theresist pattern is transferred to the second layer by chlorine-based dryetching containing oxygen, to obtain a second layer pattern. Next, theobtained second layer pattern is used as an etching mask, and the secondlayer pattern is transferred to the phase shift film by fluorine-baseddry etching, to obtain a phase shift film pattern. In case where a partof the second layer is needed to be remained, another resist patternthat protects such part to be remained is formed on the second layer,and a part of the second layer not protected with the resist pattern isremoved by chlorine-based dry etching containing oxygen. The resistpattern is then removed by a usual method to obtain the phase shiftmask.

From an exemplary phase shift mask blank including a light shieldingfilm or a combination of a light shielding film and an antireflectionfilm, composed of a chromium-containing material, as a second layer on aphase shift film, and a process-aid film composed of asilicon-containing material as a third layer on the second layer, thephase shift mask may be manufactured typically by the followingprocesses.

First, an electron beam resist film is formed on the third layer of thephase shift mask blank, a pattern is drawn by electron beam, followed bya predetermined operation of development, to obtain a resist pattern.Next, the obtained resist pattern is used as an etching mask, and theresist pattern is transferred to the third layer by fluorine-based dryetching, to obtain a third layer pattern. Next, the obtained third layerpattern is used as an etching mask, and the third layer pattern istransferred to the second layer by chlorine-based dry etching containingoxygen, to obtain a second layer pattern. The resist pattern is thenremoved, and the obtained second layer pattern is used as an etchingmask, and the second layer pattern is transferred to the phase shiftfilm by fluorine-based dry etching, to obtain a phase shift film patternand to concurrently remove the third layer pattern. Next, another resistpattern that protects a part of the second layer to be remained isformed on the second layer, and a part of the second layer not protectedwith the resist pattern is removed by chlorine-based dry etchingcontaining oxygen. The resist pattern is then removed by a usual methodto obtain the phase shift mask.

Meanwhile, from an exemplary phase shift mask blank including aprocess-aid film composed of a chromium-containing material as a secondlayer on a phase shift film, and a light shielding film or a combinationof a light shielding film and an antireflection film, composed of asilicon-containing material, as a third layer on the second layer, thephase shift mask may be manufactured typically by the followingprocesses.

First, an electron beam resist film is formed on the third layer of thephase shift mask blank, a pattern is drawn by electron beam, followed bya predetermined operation of development, to obtain a resist pattern.Next, the obtained resist pattern is used as an etching mask, and theresist pattern is transferred to the third layer by fluorine-based dryetching, to obtain a third layer pattern. Next, the obtained third layerpattern is used as an etching mask, and the third layer pattern istransferred to the second layer by chlorine-based dry etching containingoxygen, to obtain a second layer pattern that a part where the phaseshift film will be removed has been removed. The resist pattern is thenremoved. Next, another resist pattern that protects a part of the thirdlayer to be remained is formed on the third layer, and the obtainedsecond layer pattern is used as an etching mask, and the second layerpattern is transferred to the phase shift film by fluorine-based dryetching, to obtain a phase shift film pattern, and to concurrentlyremove a part of the third layer which is not protected with the resistpattern. The resist pattern is then removed by a usual method. Further,the part of the second layer, which is exposed in the part where thethird layer has been removed, is then removed by chlorine-based dryetching containing oxygen, to obtain the phase shift mask.

Further, from an exemplary phase shift mask blank including aprocess-aid film composed of a chromium-containing material as a secondlayer on a phase shift film, a light shielding film or a combination ofa light shielding film and an antireflection film, composed of asilicon-containing material, as a third layer on the second layer, and aprocess-aid film composed of a chromium-containing material, as a fourthlayer on the third layer, the phase shift mask may be manufacturedtypically by the following processes.

First, an electron beam resist film is formed on the fourth layer of thephase shift mask blank, a pattern is drawn by electron beam, followed bya predetermined operation of development, to obtain a resist pattern.Next, the obtained resist pattern is used as an etching mask, and theresist pattern is transferred to the fourth layer by chlorine-based dryetching containing oxygen, to obtain a fourth layer pattern. Next, theobtained fourth layer pattern is used as an etching mask, and the fourthlayer pattern is transferred to the third layer by fluorine-based dryetching, to obtain a third layer pattern. The resist pattern is thenremoved. Next, another resist pattern that protects a part of the thirdlayer to be remained is formed on the fourth layer, and the obtainedthird layer pattern is used as an etching mask, and the third layerpattern is transferred to the second layer by chlorine-based dry etchingcontaining oxygen, to obtain a second layer pattern, and to concurrentlyremove a part of the fourth layer which is not protected with the resistpattern. Next, the second layer pattern is used as an etching mask, andthe second layer pattern is transferred to the phase shift film byfluorine-based dry etching, to obtain a phase shift film pattern, and toconcurrently remove a part of the third layer which is not protectedwith the resist pattern.

The resist pattern is then removed by a usual method. Further, the partof the second layer, which is exposed in the part where the third layerhas been removed, and the part of the fourth layer exposed in the partwhere the resist pattern has been removed, are then removed bychlorine-based dry etching containing oxygen, to obtain the phase shiftmask.

EXAMPLES

Examples of the invention are given below by way of illustration and notby way of limitation.

Example 1

A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in achamber of a sputtering apparatus, and eight kinds of single-layer phaseshift films composed of SiN that have different compositions each otherwas formed thereon by using a silicon target as a sputtering target, andargon gas and nitrogen gas as a sputtering gas, under the conditions ofa discharge power of 1.9 kW, a flow rate of argon gas of 28 sccm(fixed), and a flow rate of nitrogen gas set between 19 sccm and 40sccm.

Refractive indexes n and extinction coefficients k, as an opticalconstant with respect to KrF excimer layer (wavelength of 248 nm), ofthe films were obtained. Graphs plotting refractive indexes n andextinction coefficients k with respect to flow rates of nitrogen gas areshown in FIGS. 3 and 4, respectively. The compositions of the films weremeasured by XPS (X-ray photoelectron spectroscopy, the same shall applyhereinafter). A graph plotting refractive indexes n with respect tocontent ratios N/(Si+N) (atomic ratio) is shown in FIG. 5. From FIG. 5,it was found that the flow rate indicating the highest refractive indexn corresponds to the content ratio N/(Si+N) of approx. 0.47.

Next, a 152 mm square, 6.35 mm thick 6025 quartz substrate was placed ina chamber of a sputtering apparatus, and a single-layer phase shift filmcomposed of SiN was formed thereon by using a silicon target as asputtering target, and argon gas and nitrogen gas as a sputtering gas,under the conditions of a discharge power of 1.9 kW, a flow rate ofargon gas of 28 sccm, and a flow rate of nitrogen of 27 sccm.

With respect to KrF excimer layer (wavelength of 248 nm), the phaseshift film had a refractive index n of 2.60 and an extinctioncoefficient k of 0.70, and had a phase shift of 177°, a transmittance of4.5%, and a thickness of 79 nm. A content ratio N/(Si+N) (atomic ratio),measured by XPS, was 0.49.

Example 2

A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in achamber of a sputtering apparatus, and eight kinds of single-layer phaseshift films composed of SiN that have different compositions each otherwas formed thereon by using a silicon target as a sputtering target, andargon gas and nitrogen gas as a sputtering gas, under the conditions ofa discharge power of 1.9 kW, a flow rate of argon gas of 17 sccm(fixed), and a flow rate of nitrogen gas set between 10 sccm and 30sccm.

Refractive indexes n and extinction coefficients k, as an opticalconstant with respect to KrF excimer layer (wavelength of 248 nm), ofthe films were obtained. The compositions of the films were measured byXPS. It was found that the flow rate indicating the highest refractiveindex n, which was confirmed according to the same way of Example 1,corresponds to the content ratio N/(Si+N) of approx. 0.47.

Next, a 152 mm square, 6.35 mm thick 6025 quartz substrate was placed ina chamber of a sputtering apparatus, and a single-layer phase shiftfilms composed of SiN was formed thereon by using a silicon target as asputtering target, and argon gas and nitrogen gas as a sputtering gas,under the conditions of a discharge power of 1.9 kW, a flow rate ofargon gas of 17 sccm, and a flow rate of nitrogen of 27 sccm.

With respect to KrF excimer layer (wavelength of 248 nm), the phaseshift film had a refractive index n of 2.60 and an extinctioncoefficient k of 0.60, and had a phase shift of 179°, a transmittance of6.7%, and a thickness of 80 nm. A content ratio N/(Si+N) (atomic ratio),measured by XPS, was 0.50.

Example 3

A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in achamber of a sputtering apparatus, and a single-layer phase shift filmscomposed of SiON was formed thereon by using a silicon target as asputtering target, and argon gas, nitrogen gas and oxygen gas as asputtering gas, under the conditions of a discharge power of 1.9 kW, aflow rate of argon gas of 28 sccm, a flow rate of nitrogen of 26 sccm,and a flow rate of oxygen of 1.5 sccm.

With respect to KrF excimer layer (wavelength of 248 nm), the phaseshift film had a refractive index n of 2.52 and an extinctioncoefficient k of 0.56, and had a phase shift of 178°, a transmittance of7.3%, and a thickness of 83 nm. A content ratio N/(Si+N) (atomic ratio),measured by XPS, was 0.49, and an oxygen content was 2 at %.

Comparative Example 1

A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in achamber of a sputtering apparatus, and a two-layer phase shift filmconsisting of a lower layer and an upper layer was formed by using asilicon target as a sputtering target, and argon gas and nitrogen gas asa sputtering gas, under the conditions of a discharge power of 1.9 kW, aflow rate of argon gas of 28 sccm, and a flow rate of nitrogen of 19sccm, for the lower layer (thickness: 27 nm) composed of SiN; and byusing the same target and gases under the same conditions other than achanged flow rate of nitrogen gas of 35 sccm, for the upper layer(thickness: 64 nm) composed of SiN.

With respect to KrF excimer layer (wavelength of 248 nm), the phaseshift film had refractive indexes n of 2.45 in the lower layer and 2.38in the upper layer, and extinction coefficients k of 1.5 in the lowerlayer and 0.07 in the upper layer, and had a phase shift of 177°, and atransmittance of 6.2%, however, the thickness of the film was 91 nm andthe film was formed thick. Content ratios N/(Si+N) (atomic ratio),measured by XPS, was 0.40 in the lower layer and 0.53 in the upperlayer.

Comparative Example 2

A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in achamber of a sputtering apparatus, and a single-layer phase shift filmcomposed of SiN that is a compositionally graded layer having acomposition continuously varying in a thickness direction, and havingoptical characteristics varying in the thickness direction was formedthereon by using a silicon target as a sputtering target, and argon gasand nitrogen gas as a sputtering gas, under the conditions of adischarge power of 1.9 kW, a flow rate of argon gas of 28 sccm, and aflow rate of nitrogen gas continuously varied from 19 to 45 sccm.

With respect to KrF excimer layer (wavelength of 248 nm), the phaseshift film had refractive indexes n of 2.45 at the lower surfaceadjacent to the substrate side and 2.33 at the upper surface remote fromthe substrate side, and extinction coefficients k of 1.5 at the lowersurface adjacent to the substrate side and 0.05 at the upper surfaceremote from the substrate side, and had a phase shift of 177°, and atransmittance of 6.0%, however, the thickness of the film was 87 nm andthe film was formed thick. Content ratios N/(Si+N) (atomic ratio),measured by XPS, was 0.40 at the lower surface adjacent to the substrateside and 0.53 at the upper surface remote from the substrate side.

Comparative Example 3

A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in achamber of a sputtering apparatus, and a single-layer phase shift filmscomposed of MoSiON was formed thereon by using a molybdenum silicon(MoSi) target and a silicon target as a sputtering target, and argongas, nitrogen gas and oxygen gas as a sputtering gas, under theconditions of a discharge power of MoSi target of 1.2 kW, a dischargepower silicon target of 8 kW, a flow rate of argon gas of 5 sccm, a flowrate of nitrogen of 65 sccm, and a flow rate of oxygen of 2.5 sccm.

With respect to KrF excimer layer (wavelength of 248 nm), the phaseshift film had a refractive index n of 2.25 and an extinctioncoefficient k of 0.52, and had a phase shift of 175°, a transmittance of6.2%, however, the thickness of the film was 99 nm and the film wasformed thick. A molybdenum content was 14 at %, and a content ratioN/(Si+N) (atomic ratio) was 0.56, measured by XPS.

Japanese Patent Application Nos. 2019-067113 and 2019-111054 areincorporated herein by reference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A phase shift mask blank comprising a substrate, and a phase shiftfilm thereon, the phase shift film composed of a material containingsilicon and nitrogen and free of a transition metal, wherein exposurelight is KrF excimer laser, the phase shift film consists of a singlelayer or a plurality of layers, the single layer or each of theplurality of layers has a refractive index n of at least 2.5 and anextinction coefficient k of 0.4 to 1, with respect to the exposurelight, and the phase shift film has a phase shift of 170 to 190° and atransmittance of 4 to 8%, with respect to the exposure light, and athickness of up to 85 nm.
 2. The phase shift mask blank of claim 1,wherein the single layer or each of the plurality of layers has acontent ratio N/(Si+N) within a range of 0.43 to 0.53, the ratioN/(Si+N) representing nitrogen content (at %) to the sum of silicon andnitrogen contents (at %).
 3. A phase shift mask blank comprising asubstrate, and a phase shift film thereon, the phase shift film composedof a material containing silicon and nitrogen and free of a transitionmetal, wherein exposure light is KrF excimer laser, the phase shift filmconsists of a single layer or a plurality of layers, at least part ofthe single layer or at least part of the plurality of layers has acontent ratio N/(Si+N) within a range of 0.43 to 0.53, the ratioN/(Si+N) representing nitrogen content (at %) to the sum of silicon andnitrogen contents (at %), and the phase shift film has a phase shift of170 to 190° with respect to the exposure light.
 4. A method ofmanufacturing the phase shift mask blank of claim 1, comprising the stepof: forming the phase shift film by reactive sputtering using asilicon-containing target and nitrogen gas, wherein in the forming step,a flow rate of the nitrogen gas is set to a value of −20% to +20% of theflow rate imparting the highest refractive index n, with respect to theexposure light, of the phase shift film, and maintained constant orvaried continuously or stepwise, the flow rate imparting the highestrefractive index n being obtained from varying the flow rate from lowrate to high rate.
 5. The method of claim 4, wherein in the formingstep, the flow rate of the nitrogen gas is set to the flow rateimparting the highest refractive index n, with respect to the exposurelight, of the phase shift film, and maintained constant.
 6. The methodof claim 4, wherein the sputtering is a magnetron sputtering, and thesilicon-containing target is silicon target.
 7. A method ofmanufacturing the phase shift mask blank of claim 3, comprising the stepof: forming the phase shift film by reactive sputtering using asilicon-containing target and nitrogen gas, wherein in the forming step,a flow rate of the nitrogen gas is set to a value of −20% to +20% of theflow rate imparting the highest refractive index n, with respect to theexposure light, of the phase shift film, and maintained constant orvaried continuously or stepwise, the flow rate imparting the highestrefractive index n being obtained from varying the flow rate from lowrate to high rate.
 8. The method of claim 7, wherein in the formingstep, the flow rate of the nitrogen gas is set to the flow rateimparting the highest refractive index n, with respect to the exposurelight, of the phase shift film, and maintained constant.
 9. The methodof claim 7, wherein the sputtering is a magnetron sputtering, and thesilicon-containing target is silicon target.
 10. A phase shift maskmanufactured by using the phase shift mask blank of claim
 1. 11. A phaseshift mask manufactured by using the phase shift mask blank of claim 3.